(1) Field of the Invention
The present invention relates to a controller-driver (represented by a controller-driver), a display device, and a display method for use in controlling a display screen on a mobile terminal apparatus or device, such as a cell phone, PDA (Personal Digital Assistant), and the like.
(2) Related Background Art
In recent years, with the trend toward high-performance and sophisticated portable terminals such as cell phones and PDAs, various types of information has been displayed on the screens. For example, prevalent types of cell phones are provided with an e-mail function, a Web browsing function, a photo-taking function, a movie display function, or the like in addition to a telephone communication function. Image data having a large data size is displayed on the screens of the cell phones as well as text data.
Referring to FIG. 33, the following describes a display device having a controller-driver with a built-in memory for use in a conventional cell phone or the like. The conventional display device comprises an image drawing unit 1 such as a CPU, a controller-driver 20 for receiving image data from the image drawing unit 1 and outputting it as display data, a display unit 3 in which pixels separated by data lines and gate lines are arranged in a matrix, a gradation voltage generating circuit 4 for generating a voltage for a gradation display, and a gate line drive circuit 5 for driving the gate lines of the display unit 3, the controller-driver 20 comprising a display memory 23 for storing image data, a latch circuit 24 for temporarily retaining a single line of image data, a data line drive circuit 25 for driving the data line of the display unit 3, a memory control circuit 21 for controlling read/write operations from or into the display memory according to a display memory control signal, and a timing control circuit 22 for controlling the memory control circuit 21, the latch circuit 24, and the gate line drive circuit 5 according to a timing control signal.
In the controller-driver 20 with the built-in memory having the above configuration, the display memory 23 generally has a storage capacity of one frame of image data. When the screen is not switched, the controller-driver stops an image data transfer from the image drawing unit 1 and outputs the image data stored in the display memory 23 to the display unit 3. When the screen is switched, the controller-driver sequentially stores the image data transmitted from the image drawing unit 1 into the display memory 23 and outputs it to the display unit 3 for displaying. In this connection, the portable terminal such as a cell phone has a limited size of the display unit 3 and a limited number of pixels from necessity of downsizing the entire device. Therefore, when an image file, e-mail, or the like exceeding the number of pixels of the display unit 3 is received, it is not possible to display all of the data on the display unit 3 and therefore the screen should be sequentially switched from one to another to display a whole of received information.
The screen switching display method, however, as described in Japanese Unexamined Patent Publication No. Hei 9-281950, has a problem that a user cannot understand the message immediately when a long message is transmitted by e-mail. Therefore, there is used a method in which message data is stored into the display memory as a bit map and a content of the display memory is shifted in such a way as to be correspondent to scrolling. When using the method of scrolling the display screen, high power consumption is needed if one frame of image data is stored into the display memory 23 whenever the screen is scrolled. Thereby, in the above publication, the power consumption is reduced by transferring only the image data of changed pixels from the image drawing unit 1.
Furthermore, there is a method in which a storage capacity of the display memory 23 is increased as a method of displaying an image file or e-mail exceeding the number of pixels of the display unit 3. For example, Japanese Unexamined Patent Publication No. Hei 7-295937 discloses a method of improving operationality of scrolling by storing display data in an area wider than an area of data that can be displayed on a display unit into a display memory, providing a mouse ball capable of detecting a scrolling distance and direction, and reading the scrolling information by means of an arithmetic operation unit.
When using the scroll function with the conventional controller-driver with the built-in memory as disclosed in Japanese Unexamined Patent Publication No. Hei 9-281950, however, the storage capacity of the built-in display memory is of one frame and therefore there is a need for transferring image data to be displayed anew from the CPU at every scrolling, thus causing a problem of increasing the power consumption. The increase of the power consumption is a significant problem for the portable terminal. The power supply need be large-sized to maintain the available time, thus damaging the feature of the small-sized and lightweight portable terminal.
In addition, the image data transfer from the image drawing unit 1 can be suppressed when using the scroll function by increasing the storage capacity of the display memory 23 built in the controller-driver 20. In the method, however, as disclosed in Japanese Unexamined Patent Publication No. Hei 7-295937, in which the display data in the area wider than the display area is stored in the image memory (display memory) and a display position on the image memory is shifted at scrolling, a chip area is increased by increasing the storage capacity of the display memory, thus obstructing the downsizing. Furthermore, an increase of a chip cost boosts up the device price problematically.
The present invention has been provided in view of the above problems. It is a main object of the present invention to provide a controller-driver, a display device, and a display method.